It is known that cyclic guanosine 3',5'-monophosphate (cGMP) induces an relaxation of cardiac muscle or smooth muscle and is implicated in the cellular growth of lymphocyte. However, there are reports in which cGMP is converted into inactive 5'GMP by cGMP phosphodiesterase, so the action of cGMP is lost. Therefore, compounds having inhibitory activity of cGMP phosphodiesterase will be able to maintain or increase level of cGMP and so will act as keeping a symmetrical metabolism. As such, the compounds can be effectively used in the prevention or treatment of hypertension, cardiagra, arteriosclerosis, respiratory system disease such as chronic bronchial asthma or bronchitis, etc.
U.S. Pat. No. 5,318,975 describes, as inhibitor of cGMP phosphodiesterase, 5-aminopyrimidine derivatives compounds of the following formula A: ##STR4##
wherein A.sup.1 represents hydrogen or imidazole substituted with lower alkyl, A.sup.2 represents hydrogen or lower alkyl and A.sup.3 represents imidazolecarboxylamide substituted with lower alkyl.
EP 640,599 describes, as inhibitor of cGMP phosphodiesterase, 4-aminopyrimidine derivatives compound of the following formula B: ##STR5##
wherein B.sup.1 represents 4-15 membered heterocyclic ring substituted with lower alkyl, lower alkoxy, halogen, etc., B.sup.2 represents 4-15 membered heterocyclic ring substituted with lower alkyl, lower alkoxy, halogen, nitro, ester, etc. or hydroxy(lower alkoxy), B represents 4-15 membered heterocyclic ring substituted with lower alkyl, lower alkoxy, halogen, nitro, sulfone, etc.